Correction of a spinal deformity typically requires stabilization and fixation of vertebrae in a particular spatial relationship. Surgical spinal correction procedures involve the placement of a plurality of bone pins, anchors, cables, hooks, or screws placed in adjacent vertebrae and using spinal rods to maintain a predetermined spatial relationship between the vertebrae. Such devices may be permanently implanted in the subject. However, in other cases, the devices may subsequently be removed when no longer needed.
Certain deformities of the spinal column require considerable correction, e.g., severe scoliosis of the spine. The use of conventional devices for spinal correction may necessitate a series of separate surgeries. For example, scoliosis treatment typically involves the use of rigid screw and connecting rods. Such connections fail to provide any degree of flexibility during the surgical procedure, thereby inhibiting manipulation and repositioning of the spinal vertebrae prior to locking the connecting rods into a rigid connection with the bone screws.
To ease the introduction and locking of connecting rods when building a spinal construct, polyaxial bone screws have been employed. However, polyaxial bone screws and other flexible connections may provide a range of motion that is too great in cases such as scoliosis. It may be necessary to restrict the range of motion during the spinal column manipulation process to only uniplanar or monoaxial movement of the connecting rod relative to the bone screw. Achieving proper alignment using conventional connecting rod and screw systems that fail to limit movement of a bone screw's head to a single plane or single axis of rotation may be problematic. While a rigid bone screw may facilitate spinal manipulation, attachment of the connecting rods is more difficult using such devices. Avoiding unwanted multi-axial movement of a screw head during manipulation while facilitating attachment of a connecting rod can be achieved by utilizing uniplanar or monoaxial screw heads.
Conventional surgical methods, however, are not designed to take full advantage of the employment of specialized bone screws, such as uniplanar and monoaxial bone screws. For example, many bone screws utilize a set screw or locking nut design to secure the rod to the screw. Such a locking system does not facilitate partial locking of the screw to the rod so that the relative position of the rod and the screw will remain stabile as adjustments are made to the position of that screw and other screws along the rod prior to final locking, and throughout final locking of the construct.